Abstract

A reflection seismic experiment was conducted over the Minneola complex
of oil and gas fields in Clark county, southwest Kansas in an attempt to
acquire high-resolution data that might distinguish a Morrowan-Atokan clastic
section containing thin productive sandstones near the top of a channel
fill to estuarine/marine section, from one that does not contain these sandstones.
Three lines were acquired. One was acquired along the length of a channel
while the other two crossed several channels and intersected the first line.
Interpretation of the data was aided by well control and seismic modeling
of well logs. Two wells along the lines contained sonic and density logs
and were used to generate synthetics that tied well with the seismic data.
The newly acquired seismic data also tied fairly well with previous seismic
data. The data were acquired using:

Previous well log seismic modeling suggested that frequencies between
120 and 180 Hz were needed on the high end and between 20 and 30 Hz on the
low end were needed for the experiment to work. What was obtained from the
final stack were high frequencies at the roll off point no higher than about
50-60 Hz at the depth of interest. Therefore, the final results of this
experiment combined with well log modeling suggest that the frequencies
obtained were too low for the presence of the thin sands to create a seismic
signature that was significantly different from a seismic signature created
from just shales. This conclusion was supported by data, which did not show
a significantly different seismic signature between a sand and no sand channel
of the same thickness. However, the results are somewhat inconclusive because
the combination of extremely wet conditions and electrical noise generated
from power lines and other sources resulted in a very poor signal to noise
ratio, particularly for frequencies above 60 Hz. If conditions were dryer,
the electrical noise may not have been as bad, and the results may have
been different. Another possibility for the lack of high frequency data
is the source. Although small charges typically produce high frequency data,
the source may have been too weak to get high frequencies down to and back
from the depth of investigation.

Alternatively, the low Q near surface ground conditions (loess) may have
caused absorption of much of the higher frequency signal at both source
and receiver. One result of the experiment though was the ability to roughly
determine channel thickness based on seismic amplitude. Although this is
not a totally new result, the additional data helped to better define the
channels mapped from previous seismic data, and supported the use of seismic
amplitudes for channel thickness determination. The data also suggest that
the channels may be more complex than the 2-D data illustrates. If a detailed
knowledge of the channel geometry would be useful for further development
of the field, than a 3-D survey of the area would be helpful. However, unless
another high resolution seismic acquisition method is found which could
record higher frequencies back from the depths of investigation, identifying
the thin Morrow sandstones from a pure shale section would be difficult
with reflection seismology alone.

e-mail : webadmin@kgs.ku.eduUpdated January 1999
The URL for this page is http://www.kgs.ku.edu/PRS/publication/OFR98_44/abstract.html